Saturday, July 14, 2007

Geology boring story

It's still darn tootin' miserable at the cottage, so I'm writing some more. No wonder nobody is showing up anymore! I think with the high gas prices, and soon to be higher interest rates, the cottage frenzy will take a dip. This month they were asking a million bucks for a cottage with no road access! I've seen this before, when the property boom dies. But I love miserable weather, since it becomes so quiet here.

When the kids were growing up, and we also had all the cousins, I used to tell long boring stories about science to put them asleep. Some of the kids really liked the stories and stayed up to the end, but instantly dropped off as soon as I finished.

Over at Highly Alloco-blah-blah, he tells of his work with the most ancient rocks of all – the African craton. Up here in Canada, we also have these old rocks, and it reminds me of a nice long geology story, suitable for putting kids asleep!

Over 4 billion years ago, the earth was forming. Lots of big ugly meteors were smashing into it, and it was mostly a big hot porridgey mess, with a methane atmosphere that would make Hamilton look good. Finally it started to cool, and the water could form seas. The heat kept bubbling out in the form of giant volcanoes and hotspots, but there was enough structure in place to start crystallizing out the scum. This was in the form of my favourite – silicon dioxide, and various other silicates. As an aside, if you are ever on the Atlantic coast, take a dark black rock, and a nice white rock of identical size, and heft them in your hands. You will find that the black rock is much denser (heavier), and thus lies the secret of all plate tectonics! The black rock is oceanic crust, and the white rock is formed of silicates.

This scum gathered into lumps which formed the cores of the ancient continents. They slowly accumulated other lumps and grew. Now, the great mystery of plate tectonics, which nobody ever talks about, is that these lumps travelled all over the place and liked to clump together. This was the start of the Wilson cycles. When they collided, great mountain ranges would form. Nobody talks about why they just didn't stay stuck together, but the new science of heat tectonics tells us that they just weren't thermally stable.

Lucky for us, this rock fuzz never went back into the boiling porridge, unlike the much denser oceanic basalt (the black rock). But when all the scum gathered together into one big fuzz-ball, something marvellous happened. It acted as a giant insulating blanket, and the heat built up underneath. In a hundred million years, the heat had built up so much (with a lot of volcanoes!), that the continents slid off the big expanded pimple of hot rock, and went out again.

As they were doing the back and forth dance, more and more silicate got separated out and floated to the top, forming the continents we see today. As we speak, the Atlantic ocean grows wider, but lays the seeds for its own destruction. The oceanic crust next to Halifax gets colder, and one day it will start to sink into the soup. At that time, a subduction zone may form, and the continents will head back into the big lump. I'll be gone to the great fishing hole in the sky by then.